Observations of the Sunyaev–Zel'dovich effect in the z=0.78 cluster MS 1137.5+6625




We have observed the z=0.78 cluster MS 1137.5+6625 with the Ryle Telescope (RT) at 15 GHz. After subtraction of contaminating radio sources in the field, we find a Sunyaev–Zel'dovich flux decrement of -421±60 μJy on the ≈0.65 kλ baseline of the RT, spatially coincident with the optical and X-ray positions for the cluster core.

For a spherical King-profile cluster model, the best fit to our flux measurement has a core radius θC=20 arcsec, consistent with previous X-ray observations, and a central temperature decrement ΔT=650±92 μK.

Using this model, we calculate that the cluster has a gas mass inside a inline image radius of 2.9×1013 M for an ΩM=1 universe and 1.6×1013 M for ΩM=0.3, ΩΛ=0.7. We compare this model with existing measurements of the total mass of the cluster, based on gravitational lensing, and estimate a gas fraction for MS 1137.5+6625 of ≈8 per cent.